This is more of a mystery that I would like help solving than an issue which needs to be resolved.
I'm working with an ancient ACAD 2004 setup and recently had a very odd issue with text kerning. Basically I had some old junk text styles which were cluttering up my docs and had to resort to SuperPurge to remove them. After purging the old text styles, I started having odd issues; all of my text was heavily weighted and had no kerning. It was so bad that using a wider letter like uppercase 'W' would cause the next letter to appear on top of the previous. Obviously letters were being spaced at a standard unit with no kerning whatsoever. I'm assuming that SuperPurge deleted some basic text file somewhere, which doesn't surprise me. It is a brute-force tool, after all.
Before finding a fix, I tried, of course, updating the text styles, importing text from a document that was not having the problem, and a couple of other things. Nothing worked. In fact, imported text took on the odd kerning issues.
What fixed the problem was going into Tools > Options > Files > Text Editor, Dictionary, and Font File Names > Alternate Font File and changing the alternate font file. I'm not really even sure how I ended up there or what the alternate font file is, but changing it seemed to jiggle whatever weird issue had lodged itself in the program and suddenly all my text styles started working again. I even changed the alternate font style back to what it had been before and the issue was still resolved, so it clearly had nothing to do with changing this particular setting. Something about changing the setting caused some process to reload, or Gods know what, and fix itself. In the end, I did the equivalent of banging on the box and the problem solved itself.
Weird things to note: Whatever I did seemed to cause a change across the whole program because now, when I open up an earlier version of the file that still has the weird issue, simply opening the text style manager and changing the font for one of my styles causes all of the text in my doc to start working correctly. I assure you, I tried changing the font in Style Manager about a hundred times before editing the Alternate Font File and it did nothing to fix the problem. So unfortunately, I can't really reproduce the problem or the fix. Also, I've found one font (Raavi) which still had the odd kerning.
Can anyone give me some insight into what happened, why it happened, and why what I did fixed this odd problem? Are there some more powerful tools for controlling font styles that I'm not aware of but managed to tinker with somehow? If uploading the (now fixed) file would do any good, let me know and I'll put it up.
I'm not realy sure why you got the weird kerning effect, but as you found out it would be to do with the font being used.
I suspect that somehow autocad had lost track of the font mappings and so was subitituting one without any kerning.
Just why this happened would be harder to track down.
Could be a lisp or some other add on changed the variable.
Could be a drawing not created in native Autocad.
Could just be that Acad threw a wobbly.
When you used the alternate font dialogue you forced Autocad to recover its font mapping and all became well again.
Alternate Fonts are used by Autocad when the font specifed in the drawing cannot be found, you can leave it to a default or specify which font to use to replace a particular missing font.
This missing font issue usually arises when you are using a drawing from another company, and they have used a font that you don't have on your PC.
The variable FONTALT specifies which font to use as the default substitute. (Just type it in).
If you have not set a default then when Autocad encounters an unknown font it will bring up a dialogue.
Or you can get through the menus to the dialogue box to specify alternate fonts (as you did).
If it does happen again, try to remember if you had run any lisps (custom routines) etc. shortly before, to try and work out what is causing it.
And check where the drawing originally came from and if it was drawn with Autocad itself, one if the Autocad variants, or even another cad programme and converted.
Drawings saved in Autocad format from other programmes can often have problems with fonts.
Good to hear you got it sorted out, and hope the above explains what probably happened.
Im intelligent enough to know that I dont know everything; but I'll tell you all about it anyway.